The present invention relates to a silica gel-supported catalyst component suitable for ethylene (co)polymerization, a catalyst therefrom and its use in ethylene (co)polymerization, in particular in a gas phase fluidized bed process operated in a condensed state.
It is well known that microspherical silica gels (having an average particle size of 10 to 100 microns) has been widely applied in catalysts for olefin polymerization as the carrier, especially in catalysts for olefin polymerization by a gas phase process, and silica gels which have been used currently include SYLOPOL 948, SYLOPOL 955 and XPO-2402 manufactured and marketed by Grace Corporation, USA and SD490 manufactured and marketed by Crosfield Corporation, typically having a specific surface area of about 300 m2/g or even less. When applied for supporting catalysts, the amount of the active components supported on these silica gels are limited and thus the improvements in catalytic activity are limited. For example, U.S. Pat. Nos. 4,293,673, 4,302,565, 4,302,566 and 4,303,771 disclose a series of catalysts suitable for ethylene polymerization by a gas phase fluidized bed process, in which the above mentioned silica gels are used as the carrier. Up to now, most of such commercially available catalysts are obtained by supporting a magnesium compound, a titanium compound and an electron donor onto SYLOPOL 955 silica gel and when they are used for ethylene polymerization by a gas phase fluidized bed process, the catalytic activity is typically about 3500 g PE/g Cat; however, when they are used in a gas phase fluidized bed process operated in a condensed state, the catalytic activity is substantially lowered due to the shortening of the residence time of the catalysts, thereby leading to an increase in the ash content of the resultant ethylene polymers, which in turn deteriorates the quality of ethylene polymers. Therefore, enhancing the activity of such catalysts is one of the key factors for the improvement in the quality of the ethylene polymers. If, however, only the specific surface area of silica gel is increased, on one hand, the activity of the catalysts when used for olefin polymerization is enhanced to some extent; on the other hand, the pore size of silica gel is decreased due to the increase in its specific surface area, thus other properties such as hydrogen response, copolymerizability of ethylene with other alpha-olefins and the like decrease dramatically (cf. U.S. Pat. No. 3,225,023). Therefore, taking the balance among various properties into account, the currently commercialized silica gel carrier materials for ethylene polymerization by a gas phase process is typically controlled to have a specific surface area of about 300 m2/g.
After extensive and repetitive investigation, the present inventors have found that by employing silica gels having a larger specific surface area and supporting thereon a magnesium compound, a titanium compound and an electron donor compound, as well as a halide promoter, the resultant catalyst has not only a largely enhanced activity when used for olefin polymerization, but also excellent hydrogen response and superior copolymerizability of ethylene with other alpha-olefins. Especially in the gas phase fluidized bed process operated in a condensed state, which represents an advanced process currently, the catalyst according to the present invention shows a good balance among various properties.
The object of the present invention is to provide a highly active silica gel-supported catalyst component suitable for ethylene (co)polymerization, which has overcome the disadvantages associated with the prior silica gel-supported titanium based catalyst, such as low activity and the like.
Another object of the present invention is to provide a catalyst for ethylene (co)polymerization.
Still another object of the present invention is to provide the use of the catalyst in accordance with the present invention for olefin (co)polymerization.
In its one aspect, the present invention provides a highly active silica gel-supported catalyst component suitable for ethylene (co)polymerization which is a titanium-containing active component supported on a porous inert carrier material, comprising the reaction product of at least one titanium compound, at least one magnesium compound, at least one halide promoter, and at least one electron donor, wherein said porous inert carrier material is spherical or spheroidal silica gel having an average particle size of 10 to 100 microns, a specific surface area of 300 to 1000 m2/g, a pore volume of 2.0 to 5.0 ml/g and an average pore diameter of 5 to 45 nanometers.
In its second aspect, the present invention provides a catalyst comprising the supported catalyst component in accordance with the present invention.
In its third aspect, the present invention relates to the use of the catalyst in accordance with the present invention for olefin (co)polymerization.
The catalyst component in accordance with the present invention is obtained by impregnating a carrier material with the reaction product of at least one titanium compound, at least one magnesium compound and at least one electron donor compound so as to support the reaction product onto the carrier material. It should be particularly noted that the carrier material is selected among spherical or spheroidal silica gels having a larger specific surface area, with dehydrated silica gels being preferred. The hydroxyl content on the surface is typically adjusted by controlling the conditions for heat-activating silica gels Preferably, silica gels have an average particle size of 10 to 100 microns, more preferably 20 to 80 microns, most preferably 30 to 60 microns; a specific surface area of 300 to 1000 m2/g, more preferably 400 to 800 m2/g, most preferably 600 to 800 m2/g; a pore volume of 1.0 to 6.0 ml/g, more preferably 2.0 to 5.0 ml/g; and an average pore diameter of 5 to 45 nanometers, more preferably 10 to 35 nanometers.
In the catalyst component as mentioned above, at least one halide promoter is also added. The halide promoter is a class of compounds represented by general formula Fxe2x80x94R1[R2bX(3-b)] wherein F represents a functional group which is chemically reactive with the organoaluminium compound, the titanium compound or hydroxyl groups on silica gels, such as an aldehyde group, an acyl group, a hydroxyl group, an amino group, an ester group and the like; R1 represents a divalent C1-C6 aliphatic or aromatic group which is attached to the functional group F; R2 represents hydrogen, unsubstituted or halogen-substituted C1-C6 alkyl, C3-C6 cycloalkyl or C6-C10 aromatic groups, b is 0, 1 or 2, and X is F, Cl or Br.
When F represents a hydroxyl group, said promoter is a class of halogenated alcohol, specific compound being 2,2,2-trichloroethanol (Cl3CCH2OH), 2,2-dichloroethanol (Cl2CHCH2OH), 2-chloroethanol (ClCH2CH2OH), 1,1-dimethyl-2,2,2-trichloroethanol (Cl3CC(CH3)2OH), 4-chlorobutanol (ClCH2CH2CH2CH2OH), para-chlorophenol, iso-chlorophenol, ortho-chlorophenol, 2-chlorocyclohexanol and the like, with 2,2,2-trichloroethanol, 2,2-dichloroethanol, 2-chloroethanol and 1,1-dimethyl-2,2,2-trichloroethanol being preferred.
When F represents an acyl group, said promoter is a class of halogenated acyl halide, suitable examples of such compounds being trichloroacetyl chloride, dichloroacetyl chloride, chloroacetyl chloride, o-chlorobenzoyl chloride and 2-chlorocyclohexyl carbonyl chloride, with trichloroacetyl chloride, dichloroacetyl chloride and chloroacetyl chloride being preferred.
In the catalyst component as mentioned above, the magnesium compound, the electron donor compound and the titanium compound have been described in U.S. Pat. No. 4,302,565, which is incorporated herein by reference.
In the titanium-containing catalyst component as mentioned above, the magnesium compound, the electron donor compound and the halide promoter are used in amounts of 0.5 to 50 moles, preferably 1.5 to 5 moles; 0.5 to 50 moles, preferably 1 to 10 moles; 0.5 to 50 moles, preferably 1 to 10 moles, per mole of the titanium compound, respectively.
In the catalyst component in accordance with the present invention, preferable titanium compounds are those represented by the following general formulae:
Ti(OR)4-nXn, or TiX3 
wherein R is C1-C14 aliphatic hydrocarbyl, X is F, Cl, Br or combinations thereof and n is an integer of 1 to 4. Suitable examples are selected from the group consisting of titanium tetrachloride, titanium trichloride, titanium tetrabromide, titanium tetraiodide, titanium tetrabutoxide, titanium tetraethoxide, triethoxy titanium chloride, diethoxy titanium dichloride, ethoxy titanium trichloride and mixtures thereof, with titanium tetrachloride, ethoxy titanium trichloride and titanium trichloride being preferred.
The magnesium compound which can be used is preferably those represented by general formula MgX2, wherein X is Cl, Br, I or combinations thereof. Specific examples can be magnesium dichloride, magnesium dibromide, magnesium diiodide, with magnesium dichloride being perferred.
The electron donor (ED) compound which can be used is preferably selected from the group consisting of alkyl esters of aliphatic or aromatic carboxylic acids, aliphatic ethers, cyclic ethers and saturated aliphatic ketones. Among them, alkyl esters of C1-C4 saturated aliphatic carboxylic acids, alkyl esters of C7-C8 aromatic carboxylic acids, C2-C6 aliphatic ethers, C3-C4 cyclic ethers, C3-C6 saturated aliphatic ketones are preferred. Most preferably are methyl formate, ethyl acetate, butyl acetate, diethyl ether, dihexyl ether, tetrahydrofuran (THF), acetone and methyl isobutyl ketone. These electron donor compounds can be used alone or in a mixture of two or more of them.
The catalyst component in accordance with the present invention is prepared by firstly dissolving the titanium compound and the magnesium compound into the electron donor compound to form a mother liquor and then impregnating a silica gel carrier having a larger specific surface area with the mother liquor, preferably by a process comprising the steps of:
(1) activating the silica gel carrier material in a conventional manner, preferably dehydrating at a temperature of 600xc2x0 C. for 4 hours;
(2) adding the heat-activated silica gel into a lower alkane solvent, followed by addition of an alkyl aluminum compound, and then reacting the mixture for a period of time, followed by evaporating the solvent and drying, thereby obtaining a solid powder;
(3) dissolving the titanium compound and the magnesium compound into the electron donor compound to prepare a mother liquor, wherein the titanium compound is added into the electron donor compound before or after the addition of the magnesium compound, or both the titanium compound and the magnesium compound are added simultaneously;
(4) adding the carrier material activated in step (2) into the mother liquor from step (3) and reacting them for a period of time, followed by drying to remove excess solvent, i.e. the electron donor compound, with its residual content being controlled to be in the range of 10 percent by weight to 21 percent by weight, thereby obtaining a solid material;
(5) suspending the solid material from step (4) in a lower alkane solvent and then reducing with one or more alkyl aluminum compounds, followed by drying, thereby obtaining the final catalyst component.
The lower alkane solvents used in step (2) and step (5) can be C3-C9 alkanes, preferably C5 and C6 alkanes, such as isopentane, pentane, hexane and the like.
The alkyl aluminum compounds which can be used in step (2) and step (5) are preferably those represented by general formula AlRxe2x80x2mX3-m, wherein Rxe2x80x2 can be same or different and represents C1-C8 alkyl groups, X represents a halogen, m is an integer of 1 to 3. Preferable alkyl aluminium compounds are AlEt3, Al(n-C6H13)3, AlEt2Cl, and the like.
It should be particularly noted that the halide promoter in accordance with the present invention can be incorporated into the catalyst component by any effective manner. For example, an excellent promotion effect can be achieved by adopting one of the following methods: i) adding during the treatment of the carrier material in step (2), ii) adding during step (4) for supporting the catalyst complex from step (3) onto the carrier material and iii) adding during the reduction of the catalyst in step (5).
The present invention also relates to a catalyst for ethylene (co)polymerization, which is a reaction product of the above titanium-containing catalyst component and an alkyl aluminum compound, wherein the alkyl aluminum compound used is represented by the general formula AlRxe2x80x33, in which Rxe2x80x3 can be same or different and represents C1-8 alkyl groups, one or two of which can be replaced by chlorine. Preferable alkyl aluminum compounds are AlEt3, Al(iso-Bu)3, Al(n-C6H13)3, Al(n-C8H17)3, AlEt2Cl and the like. The alkyl aluminum compounds can be used alone or in a mixture of two or more of them.
The catalyst according to the present invention is suitable for ethylene homopolymerization and copolymerization of ethylene and xcex1-olefins, with the xcex1-olefins being propylene, butene, pentene, hexene, 4-methylpentene-1, octene, and the like. The polymerization reaction can be carried out by a slurry process, a gas phase process or a solution process. The catalyst according to the present invention is more suitable for gas phase fluidized bed polymerization, especially for gas phase fluidized bed process operated in a condensed state. The polymerization temperature can be ranged from 50xc2x0 C. to 100xc2x0 C.
It should be particularly noted that by using silica gel having a larger specific surface area, the titanium content in the catalyst component is substantially enhanced while good particulate property of the catalyst is guaranteed, which provides the basis for enhancing the activity of the resultant catalyst. At the same time, by fixing the halide promoter carrying a functional group on the surface of silica gel by chemical reaction, the properties of polymers produced by using the resultant catalyst do not deteriorate due to the increase in the specific surface area of the carrier, and both the hydrogen response of the catalyst and copolymerizability of ethylene with other alpha-olefins are improved. Therefore, the disadvantages associated with the conventional silica gel-supported catalysts when used in a gas phase fluidized bed process operated in a condensed state, i.e., low catalytic activity, high ash content and low polymer quality, are overcome. The catalyst according to the present invention is especially suitable for gas phase fluidized bed process operated in a condensed state to produce high quality LLDPE resins.